1. Field of the Invention
The present invention relates to an oil or fat (hereafter referred to as “oil” merely) composition which is good in flavor, hard to be colored and high in hydrolysis stability, oxidation stability and emulsion stability even under severe conditions that heating is performed at a high temperature for a long period of time and thus can be used in various kinds of pharmaceutical preparations, foods and feeds and moreover has an excellent inhibitory effect on accumulation of body fat.
2. Related Background Art
In recent years, researches on the relationship between distribution of body fat and various life-style related diseases have been advanced. In particular, it has been shown that the accumulation of visceral fats such as intraperitoneal fat and hepatic fat has high correlation with diabetes, hyperlipidemia, hepatic diseases, hypertension, etc., to say nothing of obesity. It is accordingly important from the viewpoint of preventing and treating these diseases to reduce the body fat.
Techniques of using diglycerides as edible oils have been already disclosed (Japanese Patent Application Laid-Open No. 7-16053, U.S. Pat. No. 4,656,045, EP 0525915 and WO 96/32022, etc.), and it has been found that diglycerides have an effect to reduce the accumulation of body fat to prevent obesity (Japanese Patent Application Laid-Open No. 4-300828 and U.S. Pat. No. 6,004,611, etc.). The diglycerides are considered to inhibit increase of neutral lipid in blood, thereby reducing the accumulation of body fat.
However, a diglyceride is hydrolyzed and oxidized by heating or storage for a long period of time like triglycerides. The smoke point of the diglyceride is lowered by the influence of a fatty acid liberated by the hydrolysis to cause problems on smell during cooking and operability. In addition, problems of production of odor by deterioration, coloring, deterioration of flavor, etc. are also caused by the oxidation.
There is no extremely useful prior art for a method for improving the hydrolytic stability of an oil (triglyceride). On the other hand, as techniques for preventing oxidation, there have been proposed a method of adding any of various kinds of antioxidant to an oil for frying and a method of adding citric acid as a synergist (Theory and Practice of Fried Food, edited by Saiwai Shobo, 1976). However, in the latter method in particular, citric acid or a salt thereof is hardly soluble in oils, and so its effect has not been sufficient (Japanese Patent Application Laid-Open No. 49-86557).
On the other hand, triglycerides, particularly, triglycerides containing ω3 type unsaturated fatty acid(s) have been known to have physiological effects, for example, an antiallergic effect (Japanese Patent Application Laid-Open No. 63-36744) and an effect of preventing diseases of the circulatory system (Japanese Patent Application Laid-Open No. 61-85143). On the basis of such properties, application to foods and drinks for infants and patients of allergic diseases has been proposed (Japanese Patent Application Laid-Open No. 9-121766).
However, such highly unsaturated fatty acid-containing triglycerides are very easy to be oxidized. In Japanese Patent Application Laid-Open Nos. 4-46998 and 8-116878, etc., applications of these triglycerides to edible oils have been proposed. However, oxidation stability has not been sufficient. In order to solve such a problem, an addition of a great amount of an antioxidant has been known as a method for preventing the oxidation of triglycerides. However, antioxidants greatly soluble in a triglyceride are few, and there is a limit to use. In addition, the antioxidant effect of the few antioxidants is not sufficient even when they are used in a great amount. As another method for preventing the oxidation, powdering (Japanese Patent Application Laid-Open Nos. 9-121766 and 7-313057) or the like has been conducted. However, it has been difficult to widen a variation as a preparation. As described above, any technique for widely handling the triglycerides containing the highly unsaturated fatty acid(s) has not been yet established under the circumstances.
With respect to the oxidation stability of the highly unsaturated fatty acid-containing triglycerides and the diglycerides, there is a particularly strong demand for improvement in institutional or processing oils used under particularly severe conditions in fry works, daily dish shops, eating houses, restaurants, etc. Ascorbyl palmitate, tocopherol or the like may be used as an antioxidant in an increased amount in some cases. However, its effect is not sufficient. With respect to oils, there are problems of increase in smoke attendant on rise of acidic value, appearance discoloration and the like during cooking. With respect to fried products, there are problems of deterioration of flavor, color tone and/or appearance, and the like due to soap odor or the like based on decomposed fatty acids. More specifically, the diglycerides have a unique effect of inhibiting the accumulation of body fat and on one hand involve a problem that their uses are limited according to service conditions. On the other hand, in the highly unsaturated fatty acid-containing triglycerides, any solution to sole use at a high temperature has not been yet found from the viewpoints of oxidation stability and flavor. In addition, any technique for widely handling the highly unsaturated fatty acid-containing triglycerides has not be yet established due to great restrictions on preparations.